Gas turbines, aircraft engines, and numerous other combustion-based systems include one or more combustors that mix a working fluid such as air with fuel and ignite the fuel-air mixture to produce high temperature and pressure combustion gases. FIG. 1 shows a simplified cross-section of a combustor 10 that might be included, for example, in a gas turbine. A working fluid 12 may flow between a flow sleeve 14 and a liner 16 before reversing direction and flowing through one or more nozzles 18 into a combustion chamber 20. The nozzles 18 mix the fuel with the working fluid 12, and an ignition system 22 ignites the fuel-air mixture in the combustion chamber 20.
The ignition system 22 may comprise, for example, a sparkplug or laser that projects a spark or beam into the combustion chamber 20. Alternately, or in addition, the ignition system 22 may comprise a crossfire tube 24 that provides a flame, for example from an adjacent combustor, to the combustion chamber 20. In either event, the ignition system 22 is often located along a side of the combustion chamber 20 so that the ignition system 22 may project the spark, beam, or flame into the combustion chamber 20 approximately coincident with the fuel-air mixture to enhance the reliability of the ignition system 22.
The location of the ignition system 22 along the side of the combustion chamber 20 has several disadvantages. For example, the ignition systems 22 shown in FIG. 1 each require a penetration through the liner 16 of the combustor 10, creating a potential source of leakage and/or turbulent flow through or around the penetration. In addition, ignition systems 22 located along the side of the combustor 10 necessarily interfere with the flow of the working fluid 12 between the liner 16 and the flow sleeve 14, thereby increasing the differential pressure of the working fluid 12 across the combustor 10 which decreases the overall efficiency of the gas turbine. Both of these disadvantages, as well as others associated with side-mounted ignition systems 22, reduce the amount and/or flow rate of working fluid available to mix with the fuel in the nozzles 18. The amount of working fluid available for premixing with fuel has a direct impact on the peak flame temperatures and NOx emissions.
More recent attempts have been made to incorporate ignition systems into the breech end of the combustor 10 to reduce or eliminate any interference with the flow of the working fluid 12. However, the size and number of nozzles 18 located in the breech end of the combustor necessarily limits the surface area available for the ignition systems. As a result, an improved system and method for igniting a combustor 10 that reduces or eliminates penetrations through the side of the combustor 10 and/or interference with the working fluid 12 would be useful.